The invention relates to open power boats of the type used in fishing tournaments and other recreational boating and particularly to the hull configuration thereof.
In those vee entry boats having top speeds in excess of 70 MPH, with which the invention is particularly concerned, the choice of hull configuration necessarily involves tradeoff considerations of fuel economy on the one hand and high speed performance on the other.
At low speeds, deep vee entry hulls tend to exhibit a "bow up" attitude since the center of gravity is necessarily well aft of amidship to permit high speed planing. This "bow up" attitude, at low speed, is counteracted by the thrust of a transom mounted propulsion unit. The drive propeller must operate in "hard" water issuing from beneath the hull and across the plane of the transom. Thus, in the past, if a propulsion unit be mounted directly to the transom, it was necessary to impart sufficient negative trim to the unit to avoid cavitation due to the proximity of the drive propeller to the transom which, in turn, produces vertical thrust vectors thus reducing maximum overall performance than can be obtained with pure horizontal thrust. The alternative, a greater depth position of the drive unit, produces an unacceptable drag increase.
Fuel efficiency and decreasing time requirement for coming on plane from a low speed condition vary inversely with increasing negative trim to maintain "hard water" position of the drive propeller. One method of combating the foregoing is through the use of an angled transom and a transom step as referred to in applicants' prior U.S. Pat. No. 4,233,920. Even with the use of these hull modifications it is still necessary that the center line of the drive propeller be at the approximate depth of the hull center line to achieve hard water submergence without negative trim. Since drag increases exponentially with increasing propulsion unit submergence, a decrease of even an inch or two of submergence results in significant improvements in performance and fuel economy. The advantages in the avoidance of vertical thrust vectors from a negatively trimmed propulsion unit are obvious.
The usual method of achieving adequate hard water submergence for the drive propeller at a higher level in a pure horizontal thrust mode is to mount the propulsion unit in aft spaced relation to the transom by a special mounting plate commonly known as a "jack plate". The extra weight and expense of such a "jury rig" mounting is eliminated by the dual step hull herein disclosed. The primary purpose of the invention is to provide a hull configuration which allows a more shallow propulsion unit mounting (the center line of the drive propeller above the bottom of the hull center line) while yet assuring hard water submergence of the drive propeller in a pure horizontal thrust mode.
Another purpose of the invention is an improvement in the aft wedge configurations associated with the intermediate and outboard running surfaces to improve high speed turning characteristics and porpoising control. Typical prior art is found in applicants' prior U.S. Pat. Nos. 4,361,102 and 4,398,483.